Commitments - Summary of Commitments to Extend Credit and Standby Letters of Credit (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 332,808	$ 257,195	$ 208,303
Standby letters of credit	9,168	7,665	6,954
Mortgage interest rate lock commitments	$ 2,295	$ 1,180	$ 2,506